This invention generally relates to fluid heating apparatus, and more particularly, to a fluid heating system utilizing a heat pump capable of reliable operation at higher than normal ambient temperatures and assisted by a solar heating means.
In view of the ever decreasing supply of fossil and other nonrenewable resource fuels, reflected in the rising cost of gas and electricity, it has become increasingly desirable to attempt alternative approaches to heating hot water and other fluids in a reliable manner. One such attempt involves exploiting the energy of the sun, wherein a collection of solar panels exposed to solar energy containing a fluid heat transfer medium flowing into a heat exchange relationship with the building water supply or the like being heated.
While solar energy is known for use in heating homes and other installations, such known means are expensive and complex to control, especially due to unpredictable weather patterns. To meet projected demand during periods of low solar energy input, large capacity storage tanks and a large number of solar collecting panels are often required. Furthermore, exclusive use of solar heating systems is not feasible in many regions of the country, and conventional back-up heating systems such as electric, oil or gas heaters are necessary, thereby raising heating costs. However, since solar heating is often a reliable heating source under optimal conditions of sunlight, it would be desirable to combine a solar heating system with a heating system capable of cost-effective, reliable operation.
Heat pumps are becoming more and more widely used for heating systems. A typical heat pump extracts heat energy stored in a heat reservoir, such as the earth's atmosphere, by circulating an ambient air flow through evaporator coils charged with a refrigerant fluid, thereby effecting heating of the fluid within the coils. The heated refrigerant is then dumped into an accumulator where warm saturated vapor enters a suction line transferring the vapor to a compressor. The vapor is compressed into a high pressure and temperature refrigerant gas. The superheated gas is discharged from the compressor into a heat exchanger, effecting heat transfer to low temperature water. The hot water is used for domestic heating, hot water and other uses.
Conventional heat pumps are designed to operate in the heating mode at maximum ambient temperatures of 60.degree. F. to 70.degree. F. At higher temperatures, excessive heating of refrigerant fluid increases the temperature of the compressor shell and motor windings resulting in overloading of the heat pump system. Accordingly, at ambient temperatures in excess of 70.degree. F., conventional heat pumps cease operation and less efficient back-up conventional heaters must be relied upon for reliable heating, resulting in increased fuel costs.